1. Field of the Invention
The present invention relates to an image forming method, and, more particularly, it is concerned with improvement in the so-called heat-sensitive recording method and electrosensitive recording method of heretofore known types so as to be adaptable to high speed recording system.
In recent years, facsimiles, printers, and the like have attained very remarkable development, and there have been proposed various systems for such facsimiles and printers. Of these various recording systems, thermal recording method (heat-sensitive recording method) or electric recording method (electro-sensitive recording method) are employed in many occasions as the recording means for the abovementioned facsimiles, printers, and so forth, because of various advantages they possess such as, for example: (1) use of primary color-forming recording material; (2) no need for maintenance over a fairly long period of time; (3) low cost in the recording material, hence easiness in its handling; (4) possibility in size-reduction of the recording apparatus; (5) noiseless recording operation due to its being non-impact process; and (6) possibility of obtaining the recording system including the apparatus per se at a low cost; and so on.
2. Description of the Prior Arts
The conventionally known heat-sensitive recording method can be largely divided into the following two kinds.
The first method is as shown in FIG. 1 of the accompanying drawing, in which an arbitrary image original 101 carrying thereon a heat-absorption pattern is closely contacted to a recording paper 105 consisting of a substrate 105 made of paper, plastic, and like other materials, and a heat-sensitive recording layer 102 formed by coating such heat-sensitive material on, or impregnating the same in, the substrate 103, after which the infrared ray is irradiated over the entire surface of the recording paper to cause the heat-sensitive composition in the recording layer 102 to react in accordance with the heat absorption pattern, thereby obtaining a color-formed image 104.
The second method is as shown in FIG. 2, in which a signal generated from a power source section 201 is first transmitted to a thermal head 202 through an electrical circuit (not shown), whereby a resistor contained in this thermal head 202 generates heat, and the thus generated heat is further transmitted to the heat-sensitive recording layer 204 to form therein an image 203 in accordance with the signal generated from the power source section 201. Incidentally, the constructions of the substrate 205 and the recording paper 206 are substantially the same as those shown in FIG. 1. Besides the abovementioned two methods, there has also been known such a heat-sensitive recording method, in which an image is formed in accordance with laser beam irradiation.
On the other hand, for the conventionally known electrosensitive recording method, there have been proposed various systems such as discharge destruction method, electrolytic method, method by using heat due to the electric current conduction, and so forth. In this specification, however, one example thereof will be explained in reference to FIG. 3. That is, as shown in this figure of drawing, a voltage is applied to a recording needle, or stylus, 302 in accordance with a recording voltage to be generated from the power source 301, whereby a closed circuit is formed in the following route: the power source 301.fwdarw.the recording stylus 302.fwdarw.the recording layer 304.fwdarw.the electrically conductive layer 305.fwdarw.a feedback electrode 303.fwdarw.the power source 301, through which electric current flows. By this current flow, the recording layer beneath the recording stylus 302 changes to form the image 306. The recording layer 304 consists, generally, of an electrically conductive agent which permits passage therethrough of electric current, a color forming agent, and a binding agent. It goes without saying that this kind of electro-sensitive recording method is not limited to the embodiment shown in FIG. 3. The present invention proposes, as its technical object, a method, in which image formation is effected by changes in the color former due to the Joule heat or electro-chemical reaction from electric current conduction. The electrically conductive layer 305 consists of an vapor-deposited metal layer, a thin metal layer, an electrically conductive carbon layer, or a semiconductive metal layer.
A serious disadvantage with the heat-sensitive recording method as has been explained in the foregoing is that its recording speed is very slow in comparison with other recording methods. For instance, the heat pulse which is usually used in the recording method in FIG. 2 is of an order of 10 m sec. to 20 m sec., and even a higher one is of an order of 5 to 6 m/sec. at most.
There are two reasons which can be pointed out for such difficulty in attaining the high speed recording in the conventional heat-sensitive recording method. The one is that, in spite of transmission loss in a heat signal being great, energy consumption unavoidably increases from the point of necessity for carrying out satisfactory image recording, and, in addition, heat-resistance of the thermal head, for example, is limited, on account of which the high speed recording is principally difficult. The second point is that there was not available such heat-sensitive recording material that has high sensitivity and satisfactory shelf life.
The same defects as mentioned above have also been pointed out with the electro-sensitive recording method. That is, according to the electro-sensitive recording method as illustrated in the drawing, continuous electric current conduction is required for a period of from application of an electric signal for the image formation to the formation of such desired image. In other words, the electric current conduction time (t.sub.o) is substantially equal to the image forming time. If it is desired to form the image at a higher speed, the electric conduction time (t.sub.o) can be shortened, in principle. As the result, however, the image density inevitably lowers to produce practically useless reproduction image. Therefore, even in such conventional electro-sensitive recording method, the high speed recording was a problem.